RFR: 8303684: Lift upcall sharing mechanism to AbstractLinker (mainline) [v2]

[Jorn Vernee]

> Port of: https://github.com/openjdk/panama-foreign/pull/791 which lifts the sharing mechanism for upcall stubs to AbstractLinker. 
> 
> This also speeds up upcall stub linking:

Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:

  Remove spurious space
  
  Co-authored-by: Andrey Turbanov <turbanoff at gmail.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12883/files
  - new: https://git.openjdk.org/jdk/pull/12883/files/0355ab19..b359e2a0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12883&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12883&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/12883.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12883/head:pull/12883

PR: https://git.openjdk.org/jdk/pull/12883